HYPOTHESIS: HCO3-ATPase activity is directly related to the level of H ion secretion in the distal nephron and does not appear to change when proximal tubular H ion secretion changes. OBJECTIVES: 1) Isolation, partial purification and biochemical characterization of HCO3-ATPase in rat renal medulla and papilla. 2) Elucidation of the possible role of this enzyme system in rat brush border membranes, medulla and papilla during states in which H ion secretion is altered differentially in various parts of the nephron. Experiments suggest that HCO3-ATPase activity is related to H ion secretion in the early and late portions of the collecting duct, fragments of which are found in renal medulla and papilla homogenates, respectively. It does not appear to be involved in H ion secretion in the cortex, nor does activity correlate with systemic acid-base status and thus does not correlate with proximal tubular H ion secretion. These findings are of major significance in that they represent the first systematic investigation of the physiologic role of this enzyme in different portions of the renal tissue. There is little evidence in the literature regarding the isolation, purification, localization or characteristics of this enzyme in renal medulla and papilla. It is possible that the cortical fraction containing crude brush border membrane was not sensitive enough to detect small changes in HCO3-ATPase activity, thus the enzyme will be isolated from purified brush border membranes. 3) Chronic experiments will be designed which will alter H ion secretion in the distal nephron in different directions while maintaining similar systemic acid-base status. 4) HCO3-ATPase will be isolated and characterized kinetically in vesicles isolated from turtle bladder mucosa (collecting duct model) during chronic metabolic acidosis and alkalosis.